U.S. patent application number 16/307099 was filed with the patent office on 2020-10-01 for improvements relating to the interconnection of multiple renewable energy power plants.
This patent application is currently assigned to VESTAS WIND SYSTEMS A/S. The applicant listed for this patent is VESTAS WIND SYSTEMS A/S. Invention is credited to Vajira Suminda GANEPOLA, Manoj GUPTA, Ravi KUMAR, Kouroush NAYEBI.
Application Number | 20200313440 16/307099 |
Document ID | / |
Family ID | 1000004930515 |
Filed Date | 2020-10-01 |
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United States Patent
Application |
20200313440 |
Kind Code |
A1 |
GUPTA; Manoj ; et
al. |
October 1, 2020 |
IMPROVEMENTS RELATING TO THE INTERCONNECTION OF MULTIPLE RENEWABLE
ENERGY POWER PLANTS
Abstract
A power plant control system for a first renewable energy power
plant comprising one or more renewable energy generators. The power
plant control system comprises receiving means for receiving a
power delivery demand from a transmission grid operator; control
means configured to control the one or more renewable energy
generators of the first renewable energy power plant so as to
supply power that targets the received power delivery demand; and
communication means configured to transmit a request to one or more
further renewable energy power plant control systems to request
operation of one or more power compensation units associated with
respective ones of the further renewable energy power plants.
Inventors: |
GUPTA; Manoj; (Singapore,
SG) ; KUMAR; Ravi; (Sengkang, SG) ; NAYEBI;
Kouroush; (Ikast, DK) ; GANEPOLA; Vajira Suminda;
(Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VESTAS WIND SYSTEMS A/S |
Aarhus N |
|
DK |
|
|
Assignee: |
VESTAS WIND SYSTEMS A/S
Aarhus N
DK
|
Family ID: |
1000004930515 |
Appl. No.: |
16/307099 |
Filed: |
May 31, 2017 |
PCT Filed: |
May 31, 2017 |
PCT NO: |
PCT/DK2017/050181 |
371 Date: |
December 4, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J 2300/28 20200101;
H02J 3/46 20130101; H02J 3/381 20130101; H02J 2300/40 20200101;
H02J 13/00002 20200101; H02J 13/00006 20200101; H02J 2310/18
20200101; H02J 2300/24 20200101 |
International
Class: |
H02J 3/38 20060101
H02J003/38; H02J 3/46 20060101 H02J003/46; H02J 13/00 20060101
H02J013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 13, 2016 |
DK |
PA201670425 |
Claims
1. A power plant control system for a first renewable energy power
plant comprising one or more renewable energy generators, the power
plant control system comprising; receiving means for receiving a
power delivery demand from a transmission grid operator; control
means configured to control the one or more renewable energy
generators of the first renewable energy power plant so as to
supply power that targets the received power delivery demand; and
communication means configured to transmit a request to one or more
further renewable energy power plants to request operation of one
or more power compensation units associated with respective ones of
the further renewable energy power plants.
2. The power plant control system of claim 1, wherein the first
renewable energy power plant comprises power compensation units and
wherein the power plant control system is operable to control said
power compensation units.
3. The power plant control system of claim 1, wherein the
communication means includes an energy management network that
permits communication between the power plant control system of the
first renewable energy power plant, and respective power plant
control system of the one or more further renewable energy power
plants.
4. The power plant control system of claim 1, wherein the first
renewable energy power plant and the one or more further renewable
energy power plants are coupled to the same collector bus by
respective feeder lines.
5. The power plant control system of claim 1, wherein the one or
more further renewable energy power plants includes a wind energy
power plant and a photo-voltaic power plant.
6. The power plant control system of claim 1, wherein the one of
more power compensation units are one or more of the following: a
capacitor bank; a reactor bank; a static compensator (STATCOM), an
online tap changer transformer, and a device for initiating low
power production mode of an associated power plant.
7. The power plant control system of claim 6, including voltage
detection means comprising at least a first voltage measuring
device for measuring the voltage at the first renewable energy
power plant and one or more further voltage measuring devices for
measuring voltages at respective ones of the further renewable
energy power plants.
8. The power plant control system of claim 7, wherein the power
plant control system is operable to monitor the voltages at the or
each further renewable energy power plant; monitor an active power
demand from the transmission grid operator; and send a request
message via the communication means to one or more of the further
renewable energy power plants to activate capacitor banks
associated therewith.
9. The power plant control system of claim 7, wherein the power
plant control system is operable to monitor the voltage at the
first renewable energy power plant; to detect a low voltage event;
and, in response, to send a request message via the communication
means to one or more of the further renewable energy power plants
to activate capacitor banks associated therewith.
10. The power plant control system of claim 7, wherein the power
plant control system is operable to monitor the voltages at the or
each further renewable energy power plant; monitor an active power
demand from the transmission grid operator; and send a request
message via the communication means to one or more of the further
renewable energy power plants to change a tapping point of
respective online tap changer transformers associated
therewith.
11. The power plant control system of claim 1, including phasor
measurement means comprising at least a first phasor measurement
unit for measuring electrical phasor parameters at the first
renewable energy power plant and one or more further phasor
measurement units for measuring electrical phasor parameters at
respective ones of the further renewable energy power plants.
12. The power plant control system of claim 11, wherein the power
plant control system is operable to monitor the phasor measurement
means, to determine the presence of a grid fault, and in response
to send a request message via the communication means to one or
more of the further renewable energy power plants to initiate a low
power production mode of the power generation units associated
therewith.
13. A method of operating a first renewable energy power plant,
comprising: receiving a power delivery demand from a transmission
grid operator; controlling one or more renewable energy generators
of the first renewable energy power plant so as to supply power
that targets the received power delivery demand; and transmitting a
request to one or more further renewable energy power plants to
request operation of one or more power compensation units
associated with respective ones of the further renewable energy
power plants.
14. (canceled)
15. (canceled)
16. A power supply system, comprising: a first renewable energy
power plant; and a first renewable energy power plant including one
or more renewable energy generators and a power plant control
system; wherein the power plant control system comprises: a
controller configured to control the one or more renewable energy
generators of the first renewable energy power plant so as to
supply power that targets a power delivery demand received from a
transmission grid operator; and communication interface configured
to transmit a request to one or more further renewable energy power
plants to request operation of one or more power compensation units
associated with respective ones of the further renewable energy
power plants.
17. The power supply system of claim 16, wherein the first
renewable energy power plant comprises power compensation units and
wherein the power plant control system is operable to control said
power compensation units.
18. The power supply system of claim 16, wherein the communication
interface includes an energy management network that permits
communication between the power plant control system of the first
renewable energy power plant, and respective power plant control
system of the one or more further renewable energy power plants.
Description
TECHNICAL FIELD
[0001] The invention relates to the operation of a power plant
control system in a power distribution network and has particular
application to the operation of a power plant control system of a
wind energy power plant, and renewable-energy power plants more
generally.
BACKGROUND TO THE INVENTION
[0002] Penetration of wind power and other renewal forms of energy
is increasing. It is now common for newly commissioned wind power
plant installations to be able to regulate the power that they
provide to the grid. A Transmission System Operator (TSO) governs
the connection requirements of wind power plants into the grid and
defines voltage and power characteristics to which the wind power
plant must comply at a point of interconnection (POI) with the
grid. The connection requirements may comprise the grid code
requirements. A wind power plant is a group of electricity
producing wind turbine generators situated in the same geographical
location. It is also known as a wind park or a wind farm.
[0003] The operation of a wind power plant is controlled by a power
plant control system or power plant controller (PPC). The PPC
functions to receive power delivery demands from a TSO in response
to which the PPC determines appropriate active (P) and reactive
power (Q) references or `set points` to transmit to the wind
turbines under its control. PPCs are operable to monitor the grid
at the output of the power plant to ensure that these electrical
parameters are consistent with the performance demanded by the TSO.
For active power control, wind turbines in a power plant may be
operated in a curtailed mode so they can be run up to full active
power delivery as and when required. For reactive power control,
wind turbines may supply extra reactive power up to a maximum level
as governed by the operation of the converter systems used in those
wind turbines. However, further reactive power control may be
provided by additional equipment provided at a substation of an
associated power plant, such as capacitor banks, shunt reactors, or
static compensators (STATCOMs).
[0004] Due to large scale integration of renewable energy resources
into the transmission system, particularly wind power plants, grid
management is becoming more complex for TSOs. For instance,
substations associated with such power plants tend to be remote
from the main transmission grid which introduces delay in the
commands sent from the TSOs to the power plants. Furthermore, high
number of power plants being controlled by a TSO can mean that the
control is less accurate since corrective measures cannot be
carried out rapidly enough to ensure system stability. Also, even
where multiple wind power plants are connected to the grid in a
reasonably compact geographical area, all of those plants require
at least reactive compensation equipment. This increases the cost
of wind power plants which has an upwards pressure on the costs of
power generation.
[0005] It is against this background that the embodiments of the
invention have been devised.
SUMMARY OF THE INVENTION
[0006] In a first aspect, the invention provides a power plant
control system for a first renewable energy power plant comprising
one or more renewable energy generators. The power plant control
system comprises: [0007] receiving means for receiving a power
delivery demand from a transmission grid operator; [0008] control
means configured to control the one or more renewable energy
generators of the first renewable energy power plant so as to
supply power that targets the received power delivery demand;
[0009] and communication means configured to transmit a request to
one or more further renewable energy power plant control systems to
request operation of one or more power compensation units
associated with respective ones of the further renewable energy
power plants.
[0010] The invention extends to and also embraces a power system
comprising a first renewable energy power plant and one or more
further renewable energy power plants, wherein the first renewable
energy power plant includes a power plant control system as defined
above.
[0011] The invention has particular utility to wind power plants,
but also applies to other types of renewable energy power plants,
for example photo-voltaic power plants, hydro-electric power plants
and the like.
[0012] The invention also resides in a method of operating a first
renewable energy power plant, comprising: [0013] receiving a power
delivery demand from a transmission grid operator; [0014]
controlling one or more renewable energy generators of the first
renewable energy power plant so as to supply power that targets the
received power delivery demand; and [0015] transmitting a request
to one or more further renewable energy power plants to request
operation of one or more power compensation units associated with
respective ones of the further renewable energy power plants.
[0016] The invention also may be expressed as a computer program
product downloadable from a communications network and/or stored on
a machine readable medium, comprising program code instructions for
implementing a method as defined above.
[0017] An advantage provided by the embodiments of the invention is
that the power plant control system of the first renewable energy
power plant has the functionality to manage the power delivery
across multiple power plants, and therefore acts as an energy
management system, able to active assets of other power plants so
as to react quickly to any grid instabilities that may be detected.
This provides a robust response to grid instabilities.
[0018] In the illustrated embodiment, the first renewable energy
power plant also comprises power compensation units, wherein the
power plant control system is operable to control said power
compensation units.
[0019] Beneficially, the communication means permits communication
between the power plant control system of the first renewable
energy power plant, and respective power plant control system of
the one or more further renewable energy power plants. In one
embodiment, the first renewable energy power plant and the one or
more further renewable energy power plants are coupled to the same
collector bus by respective feeder lines. Alternative embodiments
are envisaged, however, where the power plants are coupled to a
distribution grid by separate feeder/transmission lines, and not
through a common collector bus.
[0020] The one of more power compensation units may comprise one or
more of the following: a capacitor bank; a reactor bank; a static
compensator (STATCOM), an online tap changer transformer, and a
device for initiating low power production mode of an associated
power plant.
[0021] In one embodiment, the system may include voltage detection
means comprising at least a first voltage measuring device for
measuring the voltage at the first renewable energy power plant and
one or more further voltage measuring devices for measuring
voltages at respective ones of the further renewable energy power
plants. Therefore, the power plant control system may be operable
to monitor the voltages at the or each further renewable energy
power plant; monitor an active power demand from the transmission
grid operator; and send a request message via the communication
means to one or more of the further renewable energy power plants
to activate capacitor banks associated therewith.
[0022] The power plant control system may also be operable to
monitor the voltage at the first renewable energy power plant; to
detect a low voltage event; and, in response, to send a request
message via the communication means to one or more of the further
renewable energy power plants to activate capacitor banks
associated therewith. Furthermore, the power plant control system
may be operable to monitor the voltages at the or each further
renewable energy power plant; monitor an active power demand from
the transmission grid operator; and send a request message via the
communication means to one or more of the further renewable energy
power plants to change a tapping point of respective online tap
changer transformers associated therewith.
[0023] In other embodiments, the power plant control system may
comprise phasor measurement means comprising at least a first
phasor measurement unit for measuring electrical phasor parameters
at the first renewable energy power plant and one or more further
phasor measurement units for measuring electrical phasor parameters
at respective ones of the further renewable energy power plants.
Accordingly, the power plant control system may be operable to
monitor the phasor measurement means, to determine the presence of
a grid fault, and in response to send a request message via the
communication means to one or more of the further renewable energy
power plants to initiate a low power production mode of the power
generation units associated therewith.
[0024] Within the scope of this application it is expressly
intended that the various aspects, embodiments, examples and
alternatives set out in the preceding paragraphs, in the claims
and/or in the following description and drawings, and in particular
the individual features thereof, may be taken independently or in
any combination. That is, all embodiments and/or features of any
embodiment can be combined in any way and/or combination, unless
such features are incompatible. The applicant reserves the right to
change any originally filed claim or file any new claim
accordingly, including the right to amend any originally filed
claim to depend from and/or incorporate any feature of any other
claim although not originally claimed in that matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] So that it may be more fully understood, the invention will
now be described, by way of example only, with reference to the
following drawings, in which:
[0026] FIG. 1 is a schematic diagram of a power generation network,
including a plurality of renewable energy power plants that are
configured to supply power to a power transmission grid;
[0027] FIG. 2 is a schematic diagram showing the a wind turbine of
a wind power plant of FIG. 1 in more detail;
[0028] FIG. 3 is a plot that illustrates the effects of a power
plant control system carrying out a response to stabilize grid
stability; and
[0029] FIG. 4 is a process flow chart depicting a method according
to an embodiment of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0030] Embodiments of the invention provide methods and techniques
for operating a power plant control system of a renewable energy
power plant, particularly a wind power plant, so as to regulate
power delivery to a power network in order to meet grid
interconnection demands. Conventionally, wind power plants are
connected to a regional or national power distribution grid by a
dedicated transmission line and are operationally separate from one
another. That is, the power plant control system of one wind power
plant has no influence over the operation of another wind power
plant. Power plant control systems associated with those respective
power plants may therefore be equipped with control strategies for
controlling the power output of the power plant in order to
regulate the power injected into the distribution grid at the point
of interconnection, or POI, at which the transmission line connects
to the distribution grid. This ensures that the actual power
delivered by the power plant at the POI meets the grid code
requirement that are dictated by a transmission system operator, or
TSO, associated with the distribution grid.
[0031] In practical terms, controlling the wind turbines of a power
plant might involve providing reference values for voltage (V),
active power (P) and reactive power (Q) for each of the wind
turbines populating the power plant. Such reference values may be
dispatched by a dispatcher of the power plant control system as
would be well understood by those skilled in the art. The reference
values dispatched may be the same for all of the wind turbines in
the power plant, taking account of any non-operational wind
turbines, as appropriate, or the reference values may be determined
for each wind turbine specifically based on a calculation that
takes into account issues such as the operating capacity of the
wind turbine, wind conditions prevailing at the specific site or
each wind turbine, the requirement for energy storage, and so
on.
[0032] Government policies have in part driven the increasing
penetration of wind power into the power generation mix in the UK
and worldwide. The planning and commissioning of large numbers of
wind power plants of various capacities, and also other forms of
renewal power generation such as photo-voltaic (PV) plants and even
wave-energy plants, means that it is not necessarily appropriate,
possible, or economically viable to connect each of those power
plants to the distribution grid by its own dedicated transmission
line. Instead, it may be desirable for multiple power plants to
feed in to the distribution grid by way of a common transmission
line. So, multiple renewable energy power plants may be coupled to
an electrical network to provide access to the common transmission
line. Such an electrical network may be referred to as a collector
bus or grid, or also a local grid. Such a collector bus may be a
single cable, for example a subterranean cable, or may be more than
one cable connected by common transmission lines, for example
overhead transmission lines. However, typically an entire collector
bus would be at the same bus voltage.
[0033] A challenge of this type of infrastructure is that the
multiple power plants coupled to the collector bus may have
different capacities, may be operated by different power companies,
and may comprise turbines from different manufacturers. Therefore,
this mix is challenging in terms of ensuring that the power
delivery at the POI of the common transmission line to the
distribution grid meets the grid specification. Determining how a
wind power plant should be operated to accommodate this complicated
mix of operational issues is not straightforward.
[0034] In the discussion that follows, an example layout of a power
network will be described in which multiple renewable energy power
plants, including wind power plants and PV plants, by way of
non-limiting examples, are connected to a common point or bus, and
are thereafter connected to a main power transmission or power
distribution grid by a common transmission line. Suitable control
strategies will also be explained that may be implemented by one of
the power plant control systems associated with a respective wind
power plant in order to regulate more effectively the power
characteristics delivered at the point of interconnection with the
main transmission grid in order that those power characteristics
or, more simply `delivered power`, match more closely the grid
specification set by a grid operator, or which may be needed to
support grid stability.
[0035] With reference now to FIG. 1, an example of a wind power
plant 10 in a wider power network 11 is shown to which control
concepts according to embodiments of the invention may be applied.
The example shown is representative only and the skilled reader
will appreciate that the methods, systems and techniques described
below may be applicable to many different configurations of power
networks. Moreover, the components of the wind power plant 10 are
conventional and as such would be familiar to the skilled reader,
and so will only be described in overview.
[0036] The wind power plant 10 shown in FIG. 1 includes a plurality
of wind turbine generators 12 or more simply `wind turbines`, but a
single wind turbine would also be possible. The wind turbines 12
are connected to a plant-level power network or `grid` 16 which, in
turn, is connected to a collector bus 18 via a first feeder line
19. The collector bus 18 provides a point of common coupling (PCC)
for a plurality of wind power plants, although only a second wind
power plant 20 is shown in FIG. 1. The collector bus 18 may be at
an intermediate voltage level that is suitable for relatively short
distance power transmission, for example in the region of 10-150
kV, most usually between 110 and 150 kV.
[0037] The collector bus 18 is connected to a power transmission
grid 24 by a transmission line 26 at a point of interconnection 27.
Whereas the collector bus 18 may be configured to network different
power plants, and so may be required to span distances up to around
100 km, the transmission grid 24 may be a regional- or
national-level network and so may be required to span distances of
up to around 250 km or more. Accordingly, the voltage level of the
transmission grid 24 may be much higher than the voltage level of
the collector bus 18 for better transmission efficiency. To put
this in context, transmission grids are usually operated in the
order of up to and even above 300 kV (usually 150-400 kV). It
should be noted that transformers that would be necessary to step
up the voltages between the collector bus 18 and the transmission
line 26 are not shown here, but their presence is implied.
[0038] Although FIG. 1 is in general a high-level schematic to
illustrate the main items in the power network 11, one of the wind
turbines 12 of the wind power plant 10 is shown schematically in
FIG. 2 for completeness, and will now be described here. The wind
turbine 12 comprises a generator 30 that is driven by a rotor (not
shown) to produce electrical power that is transmitted through a
power converter system 32 to a coupling transformer 34 via a low
voltage link 36.
[0039] Electrical power produced by the generator 30 is delivered
to the plant-level power network 16 through the coupling
transformer 34 which functions to step up the voltage generated by
the power system 32 (typically a line voltage in the order of
400-500V) to a voltage that matches the voltage of the plant-level
power network 16.
[0040] The power produced in the generator 30 is three-phase AC,
but is not in a form suitable for delivery to the plant-level power
network 16, in particular because it is typically not at the
correct frequency or phase angle. Accordingly, the power converter
system 32 includes a power converter 40 and a filter 42 disposed
between the generator 30 and the coupling transformer 34 to process
the generator output into a suitable waveform having the same
frequency as the plant-level power network 16 and the appropriate
phase angle.
[0041] The AC output of the power converter 40 is fed to the
coupling transformer 34 by way of the low voltage link 36.
Typically the low voltage link 36 will have a line voltage of below
about 1 kV, by way of example. The low voltage link 36 is depicted
here as comprising three lines, reflecting the fact that it is a
three-phase system. The power output of the power converter 40 is
conditioned by the filter 42, represented here by a suitable
inductor/capacitor network, to provide low-pass filtering for
removing high frequency noise from the AC waveform.
[0042] Modern wind turbines may have different architectures, so
the following discussion should be considered to be by way of
example only. In the illustrated example, the power converter 40
has a full-scale back-to-back power converter architecture which is
known generally in the art. As such, the power converter 40
provides full-scale AC to AC conversion by feeding electrical
current through an AC-DC converter 44 and a DC-AC converter 46
(also known as an inverter). The AC-DC converter 44 is connected to
the DC-AC converter 46 by a conventional DC link 48, which includes
a capacitor 50 providing smoothing for the DC output and a switched
resistor 52 to act as a dump load to enable excess energy to be
discharged if operational circumstances dictate that it is
necessary. The smoothed DC output of the AC-DC converter 44 is
received as a DC input by the DC-AC converter 46 which generates a
three-phase AC output for delivery to the coupling transformer 34.
As an example, another suitable architecture for a utility-scale
wind turbine would be a doubly-fed induction generator (DFIG)
converter system. As the skilled reader will appreciate, the DC-AC
converter 46 is configured to provide a level of control over the
characteristics of the AC power produced, for example to regulate
the voltage (V), the active power (P) and the reactive power (Q)
delivered by the wind turbine to the plant-level network 16 and,
thus, to the collector bus 18. From a practical point of view, it
is DFIG (also known as Type 3) and Full-scale converter (also known
as Type 4) wind turbines that are used in commercial-scale wind
power generation, and to which this discussion relates.
[0043] Noting that the magnitude, angle and frequency of the output
of the wind turbine 12 is dictated by grid requirements set by a
TSO, and that the voltage is set at a substantially constant level
in accordance with the specifications of the low voltage link 36,
in practice only the current of the AC output is controlled, and a
wind turbine controller 54 is provided for this purpose. The wind
turbine controller 54 is configured to receive target values for
the active power P.sub.REF and the reactive power Q.sub.REF
contained in the AC output, and to adjust the AC output
accordingly. As is known, the values of P.sub.REF and Q.sub.REF are
transmitted or `dispatched` to the wind turbine controller 54, by a
power plant control system 60 of the wind power plant 10. It should
be noted that the power plant control system 60 may be implemented
by a suitable configuration of hardware and software in order to
achieve its required control objectives. Moreover, it may be
implemented as a specifically designed hardware module comprising
suitable processors, memory modules and interfaces, or it may be
implemented as a general purpose computer. In either case, the
computing units or controllers may be implemented to run suitable
software algorithms to carry out the functionality that will be
described below and so will be provided with appropriate hardware
and memory.
[0044] Returning to FIG. 1, it will be appreciated that the
operation of the wind power plant 10 is responsive to the demands
of a Transmission System Operator (TSO) 70. In particular, the TSO
70 will transmit to a receiving means or receiver 69 of the power
plant control system 60 target values of voltage (V), active power
(P) and reactive power (Q) which the power plant control system 60
must try and meet when it controls the wind turbines 12 to deliver
power to the plant-level power network 16 and, from there, to the
collector bus 18 via collector substation 72.
[0045] In response to the demands placed on it by the TSO 70, the
power plant control system 60 is operable to interpret the target
voltage and power references and dispatch corresponding reference
values (V.sub.ref, P.sub.ref and Q.sub.ref) to each of the wind
turbines 12 in the power plant 10 by way of a dispatching module
60a which acts as a control means for controlling the wind turbines
12.
[0046] The power plant control system 60 is also operable to
control power compensation assets or devices that provide a further
degree of control over the active power, reactive power and voltage
that the power plant control system 60 is able to deliver to the
collector bus 18. In this embodiment, the power compensation
devices include one or more reactor banks 74, one or more capacitor
banks 76, and a transformer 78 which is provided with online tap
changer (OLTC) functionality. Other devices are possible such as
static compensators (STATCOMs). The reactor/capacitor banks 74, 76
and the transformer 78 may be located at or in the vicinity of the
substation 72 of the power plant 10. Note also that although the
power plant control system 60 is shown as separate from the
substation 72 in FIG. 1, this is merely so that the individual
components are clear and, in fact, the power plant control system
60 may be located within the substation 72.
[0047] To illustrate an example of how the power plant control
system 60 may operate, in response to the TSO 70 increasing the
reactive power reference Q.sub.ref, the power plant control system
60 may take the decision to operate its capacitor bank 76 in order
to increase reactive power if the power plant 10 has no additional
capacity to increase reactive power through operation of the wind
turbines alone. By way of further example, in the event that the
power plant control system 60 detects a drop of reactive power on
the collector bus 18, it may act to increase the reactive power
delivered to the collector bus 18 by operating the capacitor bank
76.
[0048] In addition to the functionality described above which the
power plant control system 60 implements to control its own power
generation and power compensation assets, such as the wind turbines
12, reactor bank 74, capacitor bank 76 and OLTC 78, to deliver the
target power delivery to the collector bus 18 and to help maintain
the stability of the system, the power plant control system 60 is
also operable to engage with power compensation assets of other
power plants. Thus, the power plant control system 60 can therefore
activate, or cause to be activated, power compensation devices,
including generating units, of other renewable energy power plants
in the network in order to achieve certain power delivery
objectives, for example in order to provide more reactive power of
the collector bus 18 than it can provide on its own so as to
support the stability of the collector bus 18.
[0049] Referring again to FIG. 1, it will be appreciated that the
second wind power plant 20 is substantially the same as the first
wind power plant 10 in that it comprises a plurality of wind
turbines 12 and an associated power plant control system 80 which
dispatches active and reactive power references to the wind
turbines via a dispatching module 80a. Furthermore, the second wind
turbine power plant 20 comprises respective power compensation
devices include one or more reactor banks 82, one or more capacitor
banks 84, and a transformer 88 which is provided with online tap
changer (OLTC) functionality. In this embodiment the OLTC
transformer 88 is shown within the boundary of a substation 89,
although this is not essential, and the reactor/capacitor banks
82,84 may also be contained within the substation 89. Here, the
second wind power plant 20 is shown as being connected to the
collector bus 18 by a second feeder line 86.
[0050] In addition to the second wind power plant 20, the power
network 11 is shown as also including a photo-voltaic (PV) power
plant 90 which is also coupled to the collector bus 18. In more
detail, the PV power plant includes a PV array 92, as is generally
known in the art, which is coupled via a power inverter 94 to a low
voltage AC transmission line 96. A PV plant control system 95
serves to control the operation of the power inverter 94. In order
to increase the voltage of the low voltage AC transmission line 96
to a voltage that is suitable for the collector bus 18, the
delivered power is provided to a transformer 98, which may have
OLTC functionality, at a substation 100. From the substation, the
PV power plant 20 is coupled to the collector bus 18 by a third
feeder line 102.
[0051] The PV power plant control system 95 has a degree of
flexibility to determine the voltage (V), reactive power (P) and
reactive power (Q) that the PV power plant 90 provides to the
collector bus 18 by virtue of the functionality of the power
inverter 94. However, the PV power plant 90 in this embodiment is
also provided with power compensation devices to provide it with
further capacity to control the generated active and reactive power
balance so that it can assist in supporting the stability of the
grid, as required. Here, in a similar way to the wind power plants
10, 20 of the power network 11, the PV power plant 90 also
comprises a reactor bank 104 and a capacitor bank 106, in addition
to the OLTC functionality of the transformer 98.
[0052] It should be noted that each of the second wind power plant
20 and the PV power plant 90 is able to operate independently to
deliver power to the collector bus 18 in accordance with the power
reference requirements transmitted to the control systems by the
TSO 70.
[0053] However, here it should be appreciated that the operation of
elements of all of the renewable energy power plants 10, 20, 90 are
interlinked by a communication system 110. In FIG. 1 the
communication system 110 is illustrated by a dashed line that
extends from the power plant control system 60 of the first wind
power plant 10, to the power plant control system 80 of the second
wind power plant 20, and also the PV power plant control system 95
of the PV power plant 90.
[0054] The communication system 110 comprises suitable computing
equipment at each of the power plant control systems to provide an
electronic interface to the system 110, together with a
communications link between those interfaces. The communications
link may be a wired link, for example in the form of a wide area
network (WAN), or may be wireless using a suitable messaging
protocol over a cellular telecommunications network or dedicated
point to point communications system. In addition, or
alternatively, the communication system 110 may be connected to the
various substations of each of the power plants. Information can
therefore be retrieved from the substations directly by the power
plant control system 60, acting as a `master controller` or
indirectly via each of the control systems of the respective power
plants. It is known that substations include suitable components of
a supervisory control and data acquisition (SCADA) system to allow
them to communicate with external systems such as TSOs. Thus, the
same SCADA communication components may be used to feed substation
information to the communication system 110, as indicated by dashed
lines 111.
[0055] By virtue of the communication system 110, the first power
plant control system 60 is able to transmit control request
messages to the power plant control system 80 of the second wind
power plant 20, and also the PV power plant control system 95 of
the PV power plant 90 to gain control of their power compensation
assets. This provides the first power plant control system 60 an
enhanced ability to meet its power delivery objectives and, in
particular, to support the stability of the collector grid 18 and,
more broadly, the power transmission grid 24.
[0056] In this way, the first power plant control system 60 is able
to function in a similar way to a micro-grid controller since it is
able to demand reactive power to be delivered from its neighbouring
wind power plant or PV power plant and furthermore can request
operation of the reactor banks and capacitor banks of those power
plants which supports the delivery of increased active power into
the grid. Beneficially, therefore, the power plant control system
60 acts as an energy management system since it has the
functionality to manage the power delivery across multiple power
plants. Due to the relatively close proximity of the power plants
10,20,90, the communication system 110 can be configured to provide
relatively high speed communications which allows the first power
plant control system 60 to react quickly to any grid instabilities
that it detects. This provides a more robust response to grid
instabilities than would be the case if each of the power plants
was acting along in response to commands from the TSO 70. It will
be appreciated that commands from the TSO 70 would generally be
transmitted over a SCADA system.
[0057] To illustrate the functionality provided by the embodiments
of the invention, a number of operational scenarios will now be
described.
[0058] Controlling Reactive Power Output from Nearby Power
Plant
[0059] As shown in FIG. 1, the PV power plant 90 is also connected
to the collector bus 18. The first power plant control system 60
has information on the power delivery capabilities of the PV power
plant 90, for example the maximum active and reactive power it can
provide, and at what voltage level. The power plant control system
60 is operable to monitor the stability of the collector bus 18 by
measuring the voltage at its respective substation 72. Due to a
grid event somewhere on the power network 11, it is possible that
the grid voltage may drop to a certain level, for example 0.9 pu.
Such a voltage drop is detectable by the power plant control system
60 which includes voltage measuring device 71 integrated at the
substation 72.
[0060] Further voltage measuring devices may be provided at the
other power plants 10, 20 and are marked on FIG. 1 by references 85
and 101, respectively. In one sense, therefore, the further voltage
measuring devices may be considered to form part of the first power
plant control system 60 since they provide a means for that system
to monitor grid voltages at remote points. In circumstances where
the first power plant 10 does not have any further capacity to
increase its output of reactive power, for example where the wind
turbines are at maximum capacity and where all capacitor banks are
in operation, there would be a shortfall in the capability of the
power plant control system 60 to support the stability of the grid
by increasing reactive power supply. However, by virtue of the
illustrated embodiment, the power plant control system 60 may make
a determination that further reactive power and may transmit a
request to another power plant on the power network in order to
increase the reactive power delivery thereto. For example the power
plant control system 60 may transmit a request to the power plant
control system 95 of the PV plant 90 to activate its capacitor bank
106.
[0061] Here it will be appreciated that the voltage value is
expressed as a `pu` or per-unit value, which, as is known, is unit
system in which quantities of an electrical system, in this case
voltage, are expressed as a proportion of pre-defined base
quantities.
[0062] From the above discussion, the reader will appreciate that
this functionality enables the power plant control system 60 of the
first power plant 10 to act as a `master controller` to use assets
of the other substations to add stability of the grid and meet the
required control functions such as higher reactive power supply if
needed.
[0063] Controlling Tap Changer Functionality of Transformers of
Remote Power Plants
[0064] As has been discussed above, the substations 72,89,100 of
the power plants 10,20,90 comprise transformers that include tap
changer functionality so that the voltage conversion factor of said
transformers can be adjusted by controlling the tap point of
thereof.
[0065] Under certain circumstances, it may be necessary to increase
the voltage on the power network in order to achieve a
predetermined voltage control regime to help in stabilizing the
grid voltage and aid voltage stability.
[0066] In the illustrated embodiment, the power plant control
system 60 associated with the first power plant 10 may make a rapid
decision that in those circumstances the correct approach is to
adjust the tap point of the transformers in one or more of the
substations connecting the power plants 10,20,90 to the collector
bus 18 and can issue appropriate requests messages using the
communication system 110 to one or more of the other renewable
energy power plants connected to the collector bus 18 to achieve
appropriate control over the respective transformers with OLTC
adjustment functionality. Therefore the amount of active power
delivery injected into the grid could be increased due to the
increased grid stabilization support.
[0067] Controlling Entry of Other Power Plants into Low Power
Production Mode
[0068] Network faults occur from time to time on a power network
for numerous reasons. In the illustrated embodiment, the power
plant control system 60 of the first wind power plant 10 includes
equipment for determining whether a grid fault exists.
[0069] The fault detection equipment includes a Phasor Measurement
Unit (PMU) 112 that is associated with the substation 72 of the
first power plant 10. Such PMUs are generally known in the art and
are sometimes referred to as `synchrophasors`, so a full
description of such a device is not necessary here since it would
be understood by a skilled person. As example of a PMU is the
RES670 series of products marketed by ABB AB.
[0070] The PMU 112 is operable to measure electrical parameters
associated with the wind power plant and output power delivery such
as voltage and current phase angle, power angle, frequency and
frequency rate of change with respect to a synchronised time base,
as determined by a suitable Global Positioning System (GPS).
[0071] In addition to the PMU 112 associated with the substation 72
of the first wind power plant 10, the power plant control system 60
is also in communication with PMUs located at the second wind power
plant 20 and the PV power plant 90. Thus, the substation 80 of the
second power plant 20 includes a second PMU 114 and the substation
100 of the PV power plant 90 includes a third PMU 116.
[0072] Thus, a second PMU 114 is associated with the second
substation 89 of the second wind power plant 20, and a third PMU
116 is associated with the third substation 100 of the PV power
plant 90.
[0073] The PMUs 112-116 form a wide area monitoring system (WAMS)
in communication with the power plant control system 60 of the
first power plant 10. The WAMS may be defined by separate
communications network infrastructure or may comprise the
communication system 110, as is shown here. The power plant control
system 60 of the first power plant 10 may comprise suitable
functionality to interpret the data from the PMUs 112-116 in order
to make control decisions based on the data received therefrom.
Typically, the power plant control system 60 would include a Phasor
Data Concentrator (PDC) to assimilate phasor data from the
PMUs.
[0074] The presence of the PMUs 112-116 positioned at the
respective substations 72,89,100 of the power plants enables the
power plant control system 60 to collect, store and process
critical data relating to the performance of the power network at
key points therein, namely at the feeder lines which connect each
of the substations to the collector bus 18. The power plant control
system 60 is therefore able to use the data collected by the PMUs
112-116 to detect abnormal network conditions and take action to
preserve system stability and performance. Moreover, since the
power plant control system 60 is located in a neighbouring
geographical area to the other power plants on the network, it is
able to take action quickly to engage or disengage power generation
assets of those other power plants in order to maintain system
stability.
[0075] By virtue of the PMUs 112-116 associated with the feeder
lines of their respective power plants, the power plant control
system 60 is able to ensure the phase difference in the system
between the different buses, for example, the phase angle between
the first feeder line 19 and the second feeder line 86, between the
first feeder line 19 and the third feeder line 102, or between the
second feeder line 86 and the third feeder line 102. Since phase
angle difference is an indication of the degree of power system
stability of the grid, the power plant control system 60 of the
first power plant 10 is able to determine rapidly the state of the
system at one or more points. Moreover, since PMUs usually operate
at a measurement frequency of up to 200 Hz, the power plant control
system 60 can take action very rapidly to maintain system
stability.
[0076] In addition to monitoring the phase difference between the
PMUs 112-116 in the power network 11, the power plant control
system 60 may also determine the rate of change in phase difference
between two PMU measurement points. If the rate of change of phase
difference is greater than a critical value, then this may indicate
that there is a severe disturbance or a collapse of system
stability. When a grid problem has been detected by the PMUs, the
power plant control system 60 is able take the decision to send
request messages to all of the power plants under its influence, in
this example the second wind power plant 20 and the PV power plant
90 and command them to enter a low power production mode. Such a
command form the power plant control system 60 may be configured
such that the other power plants recognise it as a high priority
request message that takes priority over any other operational
commands from the TSO 70. Advantageously, upon detecting a critical
grid condition by way of the PMUs the step of commanding all of the
power plant control systems into a low power production module, for
example of between 20% and 50% of the rated power of said
respective power plants, can occur very rapidly, within about 100
to 120 ms, for example, such that further increases in phase
differences on the grid can be avoided as will the disconnection of
those power plants from the grid. So, such a response from the
power plant control system 60 enhances the low voltage ride through
capability of the power plants connected to the collector bus 18.
This will improve a stability margin of the grid, which is
particularly useful during conditions that cannot easily be
detected as faults by power plants based simply on the voltage
measurements at their terminals, such as remote line to ground
faults.
[0077] It will be appreciated therefore that in these circumstances
the power plant control system 60 is influencing directly the power
plant control systems of other power plants to transition the power
generation assets controlled by them into a low power production
mode. Those plant control systems therefore can be considered to be
devices that initiate a low power production mode in response to an
appropriate request by the power plant control system 60.
[0078] Controlling Capacitor Banks to Support Increased Active
Power Supply
[0079] As is well understood, the supply of reactive power to a
power grid supports the delivery of active power from the power
plants connected to the grid. The delivery of active power can only
be increased for a given voltage by increasing also the reactive
power. Attempting to drive more active power into the grid at a
given voltage can have the effect of destabilizing the grid and
causing the voltage to droop.
[0080] Since the power plant control system 60 of the first power
plant 10 has supervisory control of the other power plants 20, 90
coupled to the collector bus 18, following demand from the TSO 70
for greater active power, the control system 60 can take
appropriate action to meet the demands of the TSO 70.
[0081] For example, the active power that can be pushed onto the
collector bus 18 depends in part on the voltage at each of the
substations 72,89,100. During steady state operation, if the power
plant control system 60 receives a command from the TSO 70 for a
temporary increase in active power, it may not have the ability to
drive this demand based on the operation of its own power
generation assets. Therefore the power plant control system 60 may
determine that power compensation assets of other ones of the power
plants connected to the collector bus 18 may be operated in order
to satisfy the demand for extra power delivery. In this case, the
power plant control system 60 may send a request message to either
or both of the power plant control system 80 of the second wind
power plant 20 and the power plant control system 95 of the PV
power plant 90 in order to operate their respective capacitor banks
and therefore achieve a boosted voltage on the collector bus
18.
[0082] This can be seen in FIG. 3, in which the voltage, as shown
on the vertical axis, drops to 0.9 pu as the active power is
increased, whereupon the power plant control system 60 commands
operation of the capacitor banks of the other power plants 20, 90
at point P which improves the voltage profile of the collector bus
18 which means that more active power can be pushed into it. The
skilled person will appreciate that an increase in active power on
the transmission line will also increase the reactive power losses.
This increased reactive power losses, unless counteracted by
suitable grid control, tends to cause the grid voltage to drop, as
shown by the dotted line in FIG. 3. If local reactive support from
a nearby substation is available, and as can be controlled by the
power plant control system 60 acting as a master controller, the
current equivalent to the reactive power loss is available for more
active power flow, which increases the active power capability of
the line.
[0083] The scenarios discussed above explain specific circumstances
where the embodiments of the invention are envisaged to be
particularly useful. However, the skilled person will appreciate
that the inventive concept is not limited to those specific
circumstances. FIG. 4 illustrates embodiments of the invention as a
process 200 performed by the power plant control system 60 of FIG.
1 and as is embodied by the specific situations discussed above. At
step 202, the power plant control system 60 receives a power
delivery demand from the TSO 70 and monitors grid conditions. At
step 204, the power plant control system 60 then controls its power
generation assets i.e. its wind turbines 12, reactor bank 74,
capacitor banks 76 and OLTC transformer 78 in order to target the
demanded power delivery from the TSO 70. If the power plant control
system 60 determines that it cannot, by itself, meet the power
delivery demand, or if it detects a grid instability issue, it is
operable at step 206 to control the power compensation assets of
other power plants in the power network in order to meet the power
delivery demand of the TSO 70 or to tackle grid stability
objectives.
[0084] It will be appreciated that various modifications may be
made to the specific embodiments discussed above without departing
from the inventive concept, as defined by the claims. For example,
in the above power network 11 each of the power plants 10, 20 and
90 are connected to the same collector bus 18. However, this need
not be the case and alternative power network configurations are
envisaged in which the power plants may not be connected to a
common collector bus, but may instead be connected to the
transmission line individually.
* * * * *